• Journal of Aquaculture
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• v.3 no.1
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• pp.31-37
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• 1990

Ten strains of tilapiine species from genus Oreochromis were cytogenetically studied for genetic stock identification. Both the chromosome numbers(2n=44) were identical in all 10 strains. Heteromorphic sex chromosome pair were not found in any strains. Nuclear volumes vary between O. niloticus(21.0 $\mu$ $m^3$) and O. aureus(22.4 $\mu$ $m^3$)

• Journal of Aquaculture
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• v.8 no.2
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• pp.77-83
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• 1995

The effects of six levels (0, 5, 10, 15, 20, and 25 ppm) of dietary $17\alpha-Methyltestosterone$ (MT) on sex reversal and growth of Oreochromis aureus (Steindachner) and O. niloticus (L.) were evaluated. Fifteen ppm MT produced $100\%$ male populations in both species. Both MT-treated and untreated O. niloticus grew significantly faster than their O. aureus counterparts (P<0.05).

• Development and Reproduction
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• v.15 no.4
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• pp.365-371
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• 2011

Water temperature governs various biological events in many aquatic animals including fish. Temperature changes the rates of gametogenesis and development, in some cases, is even capable of reversing fish sex. Treatments of fish with unusually high temperature are known to induce the expression of HSP70 gene. Development of an effective inhibitor for HSP70 gene expression is, thus, crucial to study the role of HSP70 in the temperature sensitive biological events. We have investigated the inhibitory effect of quercetin, 3,3',4',5,7-pentahydroxyflavon, a natural flavonid, on the expressions of HSP70 gene induced by high temperature ($36^{\circ}C$) in the Nile tilapia, Oreochromis niloticus, larvae and juveniles (10~13 cm in total length). The expression of HSP 70 gene was significantly decreased in tilapia larvae immersed in 50 ${\mu}M$ or 100 ${\mu}M$ quercetin solution for 6 hours before the exposure to high temperature (P<0.05). In particular, the level of HSP70 expression in fish treated with 100 ${\mu}M$ was as low as that of fish without high temperature treatment. Juveniles of tilapia were individually injected with 0.1 $m{\ell}$ of either 0.5 mM, 5 mM or 20 mM of quercetin solution before the exposure to high temperature. As the results, the expression of HSP70 gene in the gonad and brain of juvenile fish was significantly inhibited by the injection of 0.5 mM quercetin solution (P<0.05), but not by higher concentrations. We report, for the first time in the fish, that quercetin effectively inhibits the expression of HSP70 gene induced by high temperature and 100 ${\mu}M$ for the immersion of larvae and 0.5 mM for the injection to juvenile can be used for the effective concentrations for the study of temperature sensitive biological events in tilapia.

• Journal of fish pathology
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• v.9 no.1
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• pp.53-63
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• 1996

The present study was undertaken to investigate the physiological characteristics of the cholinergic responses in the tilapia dorsal aorta. In vessels under resting tension or precontracted with norepinephrine, acetylcholine caused only concentration-dependent vasoconstrictions. Contractile response to acetylcholine was not affected by the removal of endothelium or the application of methylene blue. Atropine, gallamine or pirenzepine shifted concentration-response curve to the right. However pirenzepine showed a similar effect on the curve only at high concentration ($1{\times}10^{-5}$M). Acetylcholine-induced vasoconstriction was not markedly influenced by indomethacin, or verapamil, but was almost abolished in the calcium-free physiological buffer solution. These results suggest that acetylcholine produces only an endothelium-independent vasoconstriction in tilapia dorsal aorta and that the contractile effect of acetylcholine is mainly mediated by the activation of $M_2$ subtype receptor, which might be associated with the extracellular calcium influx through receptor-linked calcium channel.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.31 no.5
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• pp.677-684
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• 1998

The distribution and elimination of oxolinic acid (OA) following oral (80mg/kg body weight) and bath (20 mg/$\ell$) treatment were examined in the organs and plasma of Nile tilapia (Oreochromis niloticus) on different temperatures and physiological conditions using a bioassay method. On the analysis of temperature effect, both absorption and elimination of OA after oral administration were delayed in the group at $15^{\circ}C$. but significant difference of the peak concentrations in the tissues of the groups at $15^{\circ}C$ and $25^{\circ}C$ was not revealed. However, the changes of maximam concentration, absorption and elimination rates in the tissues of fish following bath treatment depending on different temperatures were more significantly different from the results of the studies with oral administration. The pharmacokinetics of OA in the tissues of diseased fish, the main target of drug treatment, also appeared to be distinguishable from those of healthy fish.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.34 no.3
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• pp.194-198
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• 2001

The study was conducted to investigate the changes of hepatic cytochrome P450 monooxygenase system induced by dietary administration of polychlorinated biphenyls (PCBs) in the tilapia, Oreochromis niloticus. Tilapia were fed pellet with PCBs (Aroclor 1254) 0.05, 0.25 and 0.50 mg/kg body weight/day for 30 days. The dietary administration of PCBs (0.05 mg/kg) induced a significantly increased the concentration of cytochrome P450 and the activity of 7-ethoxyresorufin-O-deethylase (EROD) in the hepatopancreas at 30 days, while the augmentation of both responses was found at 20 days with a higher administration of PCBs-diet (0.25 mg/kg). However, hepatic 7-penthoxyresorufin-O-dealkylase (PROD) activity did not show any noticeable changes with the PCBs-diet 0.05-0.5 mg/kg range compared to control group during the experimental periods of 30 days in the tilapia. These results indicate that tilapia fed PCBs at the concentration of more than 0.05 mg/kg for 30 days are affected by PCBs in terms of cytochrome P450 concentration and EROD activity in the hepatopancreas.

• Development and Reproduction
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• v.10 no.3
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• pp.197-202
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• 2006

Sex steroids are generally considered as natural sex inducers in fish, and aromatase (cytochrome P450 aromatase) that catalyzes androgens into estrogens in the steroidogenic pathway is also known to be involved in sex differentiation. The timing of aromatase action is, thus, of central importance in the study of fish sex differentiation. We treated sexually undifferentiated tilapia (Oreochromis niloticus) larvae with $Fadrozole^{TM}$, a non-steroidal aromatase inhibitor (AI), by immersing the fish in a solution containing AI during the sex differentiation period to narrow down the critical period of aromatase action. Fish were treated once at 11 or 13 days post fertilization (dpf), or twice at 11 and 13 dpf. The concentrations of AI at each time of the treatment were 0 mg/L (control), 50 mg/L or 100 mg/L. Survival rate was not statistically associated with AI immersion treatment (p>0.25). However, sex ratio was significantly altered by the treatment, with higher concentration and double immersion being more effective in masculinizing genetic females (p<0.05). These results suggest that aromatase action for sex differentiation in this fish species would begin at least from 11 dpf which is much earlier than previously expected, and that only 3 hours of brief immersion in AI solution is powerful enough to alter genetically programed sex.

• Journal of Aquaculture
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• v.5 no.2
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• pp.157-165
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• 1992

Experiments were conducted to find out suitable dietary lipids in the practical feed for Nile tilapia, Oreochromis nilotius. Soybean oil, corn oil, fish oil or cuttlefish liver oil was mixed in the diet and tested. The best weight gain and feed efficiency were obtained from the fish fed soybean oil or corn oil, both rich in 18 : 2n-6. But the growth rate of fish fed diet with fish oil or cuttlefish liver oil were inferior. The levels of 20 : 3n-9 in the total lipid were not different in all tested lipids, but that in the polar lipid of the fish oil or cuttlefish liver oil were lower than that in the soybean oil or corn oil. Thus, vegetable oil such as soybean oil or corn oil, rich in 18 : 2 n-6, were suitable as dietary lipid for Nile tilapia. Unlike other fish species, fish oil or cuttlefish liver oil showed no essential dietary value for this species.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.45 no.6
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• pp.675-678
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• 2012

The study examined the effect of levamisole on the natural cytotoxic cell (NCC) activity of Nile tilapia (Oreochromis niloticus) head kidney (HK) leukocytes. In vitro, HK leukocytes were incubated with $10^{-4}$ to $10^4$ ng of levamisole/ml for 5, 20 or 40 h and then their NCC activity against target cells was assayed. The NCC activity appeared to increase after a 20 h of incubation. In vivo, tilapia were fed commercial diet containing 0, 50, 100 or 300 mg of levamisole/kg for 12 consecutive days. Then, the fish were fed a commercial normal diet and samples harvested weekly 0 to 8 weeks after levamisole administration. The NCC activity was augmented uniformly at all times examined until the end of the experiment. In conclusion, levamisole effectively enhanced and maintained tilapia NCC activity.

• Journal of fish pathology
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• v.5 no.1
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• pp.9-18
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• 1992

In order to know the defense mechanism of fish, bactericidal activity was examined into the sera of carp Cyprinus carpio, tilapia Oreochromis niloticus and flounder Paralichthys olivaseus. Each examined normal serum of fishes showed the bactericidal activity against avirulent Escherichia coli but it wasn't appeared against virulent Edwardsiella tarda. When the normal serum of each fish was treated with zymosan, it lost the bactericidal activity completely. After addition of EGTA into the normal serum of each fish, the sera of tilapia and flounder still exhibited the bactericidal activity but the serum of carp lost it. In the presence of specific antibody and complement, bactericidal activity of each antiserum was exhibited high level with in one hour incubation. On the other hand, heat inactivated antiserum showed bacteriostatic reaction. From the above results, although the activity of alternative or classical pathway of each fish complement is different, it is an important function in fish defense mechanism.